The evolution of monitor technology has been swift and transformative, introducing displays with varied shapes, sizes, and capabilities tailored for both content creation and consumption. Key image quality attributes like resolution, color volume, peak brightness, and black level are critical, yet the foundational backlight and panel technology underpinning these displays often goes unnoticed. This foundation is essential for understanding the diverse landscape of modern displays, which primarily revolve around Liquid Crystal Displays (LCD), Organic Light Emitting Diode (OLED), and the emerging Quantum Dot OLED (QD-OLED) technologies. Each technology offers unique benefits and challenges, shaping the visual experience for users across devices from professional-grade reference monitors to everyday desktop, television, and mobile screens.

In this article we'd like to provide some insights into the following technologies:

• Liquid Crystal Display (LCD)
• Local vs. Global Dimming
• Dual-Layer LCDs
• Organic Light Emitting Diode (OLED)
• Quantum Dot OLED (QD-OLED)

Liquid Crystal Display (LCD)

LCD displays have been rampant in the market for decades. The main distinction of this display type is the liquid crystal layer that (combined with polarizers) modulates light emitted from a backlight source to create the final image on screen.

Because the backlight in these monitors is typically composed of an array of light emitting diodes (LEDs) the nomenclature of these display types can be confusing as LCD displays are often also referred to as LED displays (while a more accurate distinction would be an LCD panel with LED backlight).

Because the backlight of these displays is always on and the LCD layer is used to modulate or block light getting through the screen, LCD displays typically struggle with reproducing deep black levels and poor off-axis performance – meaning that as you change the viewing angle from center, the display incurs color hue and luminance shifts (which could be detrimental to color-critical work such as color grading or quality control).

 

Local vs. Global Dimming

In an effort to help LCD displays produce more acceptable images for HDR content, a technology referred to as local or global dimming is often implemented.
 

Local dimming

For displays that employ local dimming, the backlight unit is divided in ‘zones’ which can individually increase or decrease (dim) in brightness, allowing for an increase in perceived dynamic range. For example, when there is a dark area of the frame, the zones around that area in the backlight would dim or shut off to produce a deeper black. Likewise, for bright areas of the frame, the backlight zones corresponding to that portion of the image would increase in brightness, helping to better produce specular highlights.
 

Local dimming is a widely accepted technology but is quite varied in how it’s implemented. Both the number of physical zones as well as the algorithm that controls their behavior can have a significant effect on the overall display performance. For example, if a display has an inadequate number of local dimming zones or a poorly optimized algorithm, artifacts can begin to manifest themselves in areas of stark contrast (such as white text on black backgrounds, star fields, etc.). These are often referred to as ‘blooming’ or ‘haloing’ artifacts.
 

Global dimming

Global dimming refers to an implementation without any individual zones. With a global implementation, the entire backlight will brighten or dim depending on the scene or shot. This has serious implications for color-critical work as the display’s overall luminance is constantly changing.
 

Global dimming example (certain areas of backlight cannot individually change)

Dual-Layer LCDs

A newer LCD technology is referred to as dual-layer (or dual-cell) LCD. In this design, a second ‘light modulating’ layer is placed between the backlight and original LCD layer. This second layer aims to emulate local dimming by physically blocking or modulating the amount of light that passes through. The light modulating layer is individually controllable (allowing for pixel-level control) that gives advantages in black level and overall contrast ratios over traditional single layer LCDs.
 

Organic Light Emitting Diode (OLED)

OLED technology has significantly impacted display markets with its innovative approach to image production. Unlike traditional displays that require a backlight, OLED displays are composed of self-emitting pixels, each capable of producing its own light. This fundamental difference allows for much thinner designs, exceptional black levels due to the ability of pixels to turn off completely, and enhanced contrast ratios, with each pixel acting as its own dimming zone. Furthermore, OLED improves viewing angles dramatically, maintaining color accuracy and consistency across a broad spectrum of viewing positions. Within the OLED category, there are two primary types: WOLED (White OLED) and RGB OLED, each with distinct manufacturing processes and performance characteristics.

WOLED (White OLED)

WOLED technology involves the use of white organic light-emitting diodes to generate light. A key feature of WOLED displays is the color filter array placed in front of the white OLED layer, which separates the white light into RGB (red, green, and blue) components. This process is somewhat akin to how traditional LCDs operate but without the need for a backlight. The major advantage of WOLED is its simplicity in manufacturing and uniformity in brightness and color across the display. WOLED is predominantly used in large-screen TVs and some types of monitors, offering excellent color accuracy, energy efficiency, and contrast ratios. However, since it relies on a color filter, some light efficiency is lost compared to directly emitting RGB OLED displays.

RGB OLED

RGB OLED displays, on the other hand, employ individual red, green, and blue OLED sub-pixels to create the full spectrum of colors. This direct emission of color from each pixel results in more vibrant colors and higher efficiency than WOLED, as there's no loss of light through a color filter. The manufacturing process for RGB OLED is more complex, requiring precise control over the deposition of organic materials for each sub-pixel. This complexity often leads to higher production costs, especially for large displays. RGB OLED is frequently used in smaller devices, such as smartphones and tablets, where its color vibrancy and efficiency are most advantageous.

Differences Between WOLED and RGB OLED

The primary difference between WOLED and RGB OLED lies in their approach to color production. WOLED uses a white light source combined with a color filter, offering a simpler manufacturing process but at the expense of some light efficiency. RGB OLED, with its direct emission of colored light from each pixel, boasts higher vibrancy and energy efficiency but comes with increased manufacturing complexity and cost. Both technologies share the core benefits of OLED, including deep blacks and wide viewing angles, making the choice between them a matter of application, cost, and desired display characteristics.